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FOODBORNE ILLNESS AND OUTBREAK
INVESTIGATION MANUAL
March 2008
Kansas Department of Health and Environment Division of
Health
Office of Surveillance and Epidemiology
1000 SW Jackson, Suite 210 Topeka, KS 66612
24-Hour Technical Assistance: (877) 427-7317 Fax: (877)
427-7318
[email protected] www.kdheks.gov/epi
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PREFACE The Foodborne Illness and Outbreak Investigation Manual
(March 2008) is an inclusive update of the previous foodborne
disease outbreak investigation manuals first developed in 1997.
This revised version provides more detail about the epidemiologic
tools used during outbreaks investigations, offers more guidance
with regards to clinical specimen and food sample collection, and
includes a section on intentional contamination. Improvements have
been made based on user input. Comments, questions, and suggestions
regarding this manual may be directed to Epidemiologic Services in
the Office of Surveillance and Epidemiology at the Kansas
Department of Health and Environment. We may be reached toll free
by phone at (877) 427-7317, by fax at (877) 427-7318), or by e-mail
at (EPIHotline @kdhe.state.ks.us). An electronic version of this
manual may be downloaded from http://www.kdheks.gov/epi/.
Contributing editors of this revision: Sheri A. Anderson, MS, MPH,
Epidemiologist1Cheryl Bañez Ocfemia, MPH, Senior
Epidemiologist1Mary Ella Vajnar, MT (ASCP)1Nicole Hamm, Contract
Manager2Angela Kohls, CSFP, Program Director2
1 Epidemiologic Services Section, Office of Surveillance and
Epidemiology, Kansas Department of Health and
Environment 2 Food Safety and Consumer Protection Section,
Bureau of Consumer Health, Kansas Department of Health and
Environment
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TABLE OF CONTENTS REFERENCES 8 INTRODUCTION 9 SECTION 1 ─
Foodborne Illnesses 13Characteristics of foodborne pathogens
13Foodborne transmission of pathogens and toxins 14Classifications
of foodborne illnesses 15Clinical features of foodborne illnesses
15Public health surveillance and foodborne illnesses 17Epidemiology
and foodborne illnesses 17Laboratory diagnosis of foodborne
illnesses 18Pulsed-field gel electrophoresis (PFGE) 19Food
handlers, foodborne illnesses, and public health 20
SECTION 2 ─ Foodborne Disease Outbreaks 23Defining a foodborne
disease outbreak 25Identifying foodborne disease outbreaks
25Reasons for investigating foodborne disease outbreaks 26Three
components of a foodborne disease outbreak investigation 26Roles
and responsibilities in a foodborne disease outbreak investigation
26The importance of confidentiality 29
SECTION 3 – The Epidemiologic Investigation 31Steps of an
epidemiologic outbreak investigation 33
Step 1. Determine that an outbreak has occurred 34Step 2.
Contact and coordinate with key personnel 35Step 3. Obtain clinical
specimens and food samples for laboratory testing 37Step 4.
Implement control and prevention measures 38Step 5. Define cases
and conduct case finding 38
Line list 38Case definition 40Case finding 41
Step 6. Describe the outbreak by time, place, and person
42Epidemic curves 42Maps and pictures 44Frequency tables 44
Step 7. Develop possible hypotheses 45Step 8. Plan and conduct
the epidemiologic study to test hypotheses 45
Questionnaire 46Study design 46Logistics 49
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TABLE OF CONTENTS (continued)
Step 9. Analyze the data collected and interpret results 49Step
10. Report the findings of the outbreak investigation 50
Intentional contamination of food 51
SECTION 4 – The Laboratory Analysis 53General guidelines for
clinical specimen collection 55
Stool specimens 55Vomitus specimens 57Culture isolates
58Serology for hepatitis A 58Requesting stool kits, mailers, and
submission forms 59
General guidelines for food sample collection during an outbreak
investigation 60Chain of custody procedures for food samples 62
SECTION 5 – The Environmental Assessment 65Fundamental concepts
of food microbiology 67
Potentially hazardous foods 67High-risk factors in food
preparation 68
Food inspections in Kansas 69Steps of an environmental
assessment during an outbreak investigation 69
Step 1. Determine that an outbreak has occurred 70Step 2.
Contact and coordinate with key personnel 71Step 3. Conduct food
establishment inspection 71
Identifying high-risk food preparation and handling practices
71Enforcing safe food handling practices 72Supporting the
epidemiologic investigation 72
Step 4. Conduct a Hazard Analysis Critical Control Points
(HACCP) inspection 73Step 5. Report findings 74Step 6. Revisit
establishment and conduct after action meeting 74
Intentional contamination of food 75 SECTION 6 – Appendices
Appendix A – Glossary 77Appendix B – Supplemental documents for
epidemiologic investigations 85
Foodborne Outbreak Investigation Flowchart 87 Foodborne Disease
Outbreak Checklist for Local Health Departments 89Enteric Outbreak
Worksheet 91Enteric Disease Supplemental Form 93Kansas Notifiable
Disease Form 99Kansas Notifiable Disease List 100Creating a line
list 101Creating an epidemic curve 103CDC’s “Investigation of a
Foodborne Outbreak” Form (eFORS) 105
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TABLE OF CONTENTS (continued)
Guidelines for Completing “Investigation of a Foodborne
Outbreak” Form 111Data Analyses 115Final Epidemiology Report
129
Appendix C – Supplemental documents for laboratory analysis
133Requisition Form for Ordering Stool Kits, Universal Submission
Forms, and Mailers 135KDHE Universal Laboratory Specimen Submission
Form and Instructions 137Enteric Specimen Kit Packing and Shipping
Instructions 139O & P Specimen Kit Packing and Shipping
Instructions 141Diagnostic Blood Packaging and Shipping
Instructions 143
Appendix D – Supplemental documents for the environmental
assessment 145Foodborne Outbreak Investigation Flowchart
147Foodborne Disease Outbreak Checklist for Food Inspectors
149Flowchart for Kansas Department of Health and Environment
inspectors 151Flowchart for Kansas Department of Agriculture
inspectors 153KDHE Compliant Investigation Report
155Gastroenteritis Surveillance Form for Employees 157Procedures
for Distributing and Collecting Employee Surveys 159Exclusion and
Restriction Requirements for Infected Foodhandlers 161Removal of
Exclusion and Restriction Requirements for Foodhandlers 163Hazard
Analysis and Critical Control Point (HACCP) 165
Appendix E – Foodborne Illness and Etiology Tables 169Etiologic
Agents to Consider for Various Manifestations of Foodborne Illness
171Foodborne Illnesses 173Guidelines for Laboratory Confirmation of
a Foodborne Disease Outbreak 179
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REFERENCES The Kansas Department of Health and Environment
acknowledges the following sources which served as good resources
in the development and revision of this manual: • Kansas Department
of Health and Environment. Foodborne Illness and Outbreak
Investigation Manual. Septemner 2004. • Kansas Department of
Health and Environment. 2005 Kansas Food Code. • Kansas Department
of Health and Environment. Focus on Food Safety. June 2002. •
Kansas Department of Health and Environment. “Packaging and
Shipping”.
http://www.kdheks.gov/labs/packaging_and_shipping.html. •
Massachusetts Department of Health. Foodborne Illness Investigation
and Control Reference
Manual. September 1997. • Oklahoma State Department of Health.
2002 CDN-San Outbreak Training Conference
Manual. May 2002. • Wisconsin Division of Health. Foodborne and
Waterborne Outbreak Investigation Manual.
September 2005. • International Association for Food Protection.
Procedures to Investigate Foodborne Illness.
5th ed. 1999. Reprinted 2007. • Centers for Disease Control and
Prevention. “Foodborne Illness”.
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/foodborneinfections_g.htm
• Centers for Disease Control and Prevention. “Diagnosis and
Management of Foodborne
Illnesses: A Primer for Physicians and other Health Care
Professionals.” MMWR 2004:53 (No. RR-4).
• Centers for Disease Control and Prevention. Principles of
Epidemiology in Public Health Practice: An Introduction to Applied
Epidemiology and Biostatistics. 3rd ed.
• Heymann, DL., ed. Control of Communicable Diseases Manual.
American Public Health Association. 18th ed. 2004.
• Gordis, L. Epidemiology. Saunders: 1996.
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INTRODUCTION Foodborne pathogens cause an estimated 76 million
cases of foodborne illness, 325,000 hospitalizations, and 5,200
deaths in the U. S. annually. Related medical costs and lost wages
are significant, accounting for a yearly loss of up to $17
billion1. In Kansas, the main bacterial causes of food-related
illness are Campylobacter, Salmonella, Escherichia coli O157:H7,
and Shigella. Viral pathogens, specifically Norovirus (formerly
known as Norwalk-like virus) and Hepatitis A virus, are also major
causes of foodborne illness in Kansas. Food-related and other
diarrheal illnesses remain underreported throughout the U.S.,
including in Kansas. Most diarrheal illnesses resolve within 24 to
48 hours without any medical attention. As a result, many
food-related illnesses are not diagnosed and associated foodborne
disease outbreaks are often not recognized. This poses a challenge
for public health professionals to maintain the knowledge and
resources to identify and respond to these outbreaks. This manual
is written primarily for infection control nurses, food inspectors,
and outbreak investigators for the purpose of
1. Describing the fundamental concepts related to foodborne
illnesses and outbreaks; 2. Discussing the roles and
responsibilities of key personnel when responding to foodborne
illnesses and outbreaks; and 3. Establishing guidelines for
investigating foodborne disease outbreaks in Kansas.
1 Mead, P.S., et al. "Food-Related Illness and Death in the
United States." Emerging Infectious Diseases. 1999:
5(5), pp.607-25.
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SECTION 1
Foodborne Illnesses
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FUNDAMENTAL CONCEPTS
Proper and thorough investigation of foodborne disease outbreaks
requires a solid understanding of the fundamental concepts related
to foodborne illnesses.
Foodborne illnesses refer to diseases acquired through eating or
drinking contaminated food or liquids.
Characteristics of Foodborne Pathogens The most frequent causes
of foodborne illnesses include bacteria, bacterial toxins, viruses,
and parasites. Bacteria are one-celled living microorganisms
ranging in size from 1 micrometer to 10 micrometers in length. They
are naturally found in the environment (often in a spore form) or
in various animal reservoirs. Bacteria can multiply in or on food
and cause foodborne infections in persons who consume contaminated
food or liquids. Campylobacter and Salmonella are the most reported
causes of foodborne infections. Toxins most often associated with
foodborne illnesses are poisons produced or released by certain
bacteria. (NOTE: Though certain chemicals and toxins from plants,
animals, and fungi can cause illness, this manual will focus mainly
on toxin-producing bacteria.) When ingested, bacterial toxins
usually act locally within the human body, but may spread to other
parts and damage cells, tissues, and the host immune system.
Bacillus cereus, Staphylococcus aureus, and Clostridium botulinum
are well-documented toxic foodborne agents. E. coli O157:H7 and
Shigella spp. also produce toxins that cause disease, which may
lead to severe complications. Staphylococcus aureus is the most
reported cause of foodborne intoxications. Viruses are minute
organisms that reproduce only within living cells. Nonetheless,
they can remain infectious in food and may cause foodborne
infections in humans. Hepatitis A virus and Norovirus (formerly
known as Norwalk-like virus) are the most recognized food-related
viruses. Parasites are single or multi-celled organisms with
dimensions greater than 10 micrometers. Like viruses, parasites
reproduce within host cells and cannot multiply in food. However,
many parasites develop a cyst form that is inert and resistant to
the environment. This cyst, when ingested through food or liquids,
can multiply within humans and cause foodborne infections. Giardia
lamblia is the most frequently reported foodborne parasite.
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The following table summarizes the characteristics of potential
foodborne pathogens.
CHARACTERISTICS OF FOODBORNE PATHOGENS
Bacteria Viruses Parasites Cause infections
Cause intoxications Survive in environment
Multiply in environment Multiply in host
Multiply in food Form spores Produce toxins Form cysts
Foodborne Transmission of Pathogens and Toxins Food may become
contaminated during food production and processing or during food
preparation and handling. Food production and processing: Animals
naturally harbor many foodborne bacteria in their intestines that
can cause illness in humans, but often do not cause illness in the
animals. During slaughter, meat and poultry carcasses can become
contaminated if they are exposed to small amounts of intestinal
contents. Other foods, such as fruits and vegetables, may be
contaminated if washed or irrigated with water that is contaminated
with pathogens from animal or human feces. Thorough cooking of raw
foods and washing ready-to-eat foods (i.e. foods not normally
cooked or further processed before being eaten) with clean water
can decrease the risk of infection.
Food preparation and handling: • Cross-contamination: Pathogens
naturally present in one food may be transferred to other
foods during food preparation if the same cooking equipment and
utensils are used without washing and disinfecting in between. If
the foods are ready-to-eat foods, contamination can lead to
illness.
• Infected individuals: Most foodborne pathogens are shed in the
feces of infected persons and
these pathogens may be transferred to others via the fecal-oral
route. In other words, infected individuals, who do not adequately
wash their hands after using the toilet, may contaminate the
ready-to-eat food that they handle. Even minute quantities of
feces, not visible to the naked eye, may contain many pathogens and
cause illness. Bacteria present in pus-filled
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lesions and found naturally in mucous membranes of the nose may
also be transmitted from the hands of an infected foodhandler to
ready-to-eat food.
• Inadequate cooking or improper holding temperatures: Under
optimal conditions, bacteria may multiply and produce toxins within
food. Bacterial toxins that are produced are heat stable and may
not be destroyed by cooking temperatures.
Classifications of Foodborne Illnesses Foodborne illnesses are
classified as infections or intoxications. Foodborne infections are
caused by consuming foods or liquids contaminated with bacteria,
viruses, or parasites. These pathogens cause infection in one of
two ways: • Invading and multiplying in the lining of the
intestines and/or other tissues. • Invading and multiplying in the
intestinal tract and releasing a toxin (Bacteria only). Foodborne
intoxications are caused by consuming foods or beverages already
contaminated with a toxin. Sources of toxins are as follows: •
Certain bacteria. (NOTE: Viruses and parasites cannot cause
intoxications.) • Poisonous chemicals. • Natural toxins found in
animals, plants, and fungi. Clinical Features of Foodborne
Illnesses The symptoms of most foodborne illnesses include
diarrhea, nausea, vomiting, and abdominal cramping. Often
mistakenly called the “stomach flu”, these symptoms appear on
average 24 to 48 hours after infection and last for about 1 to 2
days. Appendix E provides tables that are useful in determining
potential causes of foodborne illnesses. Incubation periods are
important clues when determining possible causes of disease. For
most diseases, infected individuals can transmit pathogens during
the incubation period, when they show no symptoms of illness. For
example, an individual, who is infected with the Hepatitis A virus,
can shed the virus in stool (feces) and pass the virus to others
two weeks before clinical signs appear or the person feels ill.
The fecal-oral route of transmission describes the ingestion of
stool from an infected person or animal through food, water, or
direct contact.
Incubation period refers to the interval from the time an
individual is infected to the time when symptoms first appear.
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The recovery path that follows a foodborne illness can vary
according to the pathogen, individual host factors, and
antimicrobial use. Antimicrobial use may even shorten or lengthen
the recovery period, depending on the pathogen. Similar to the
incubation period, individuals may continue to shed the organism in
their stool during the recovery period and can potentially infect
others.
Recovery period refers to the period when symptoms decline and
illness improves.
Individuals who harbor an infectious agent but are asymptomatic
(i.e. show no symptoms of illness) are considered to be in the
carrier state. Individuals who are in the incubation period or
recovery period of an illness are known as carriers.
The following table summarizes the characteristics of infections
versus intoxications.
INFECTIONS vs. INTOXICATIONS
Infections Intoxications Organism Bacteria
Virus Parasite
Toxin
Mechanism Invade and multiply within the lining of the
intestines
No invasion or multiplication
Incubation period Hours to days Minutes to hours
Symptoms Diarrhea Nausea Vomiting Abdominal cramps Fever*
Vomiting Nausea Diarrhea Double vision Weakness Respiratory
failure Numbness Sensory and motor dysfunction
Transmission Can be spread person-to-person via the fecal-oral
route
Not communicable
Factors related to food contamination
Inadequate cooking Cross-contamination Poor personal hygiene
Bare hand contact
Inadequate cooking Improper holding temperatures
* The lack of fever in foodborne intoxications may aid
investigators when determining the cause of the foodborne illness
that is being observed.
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Public Health Surveillance and Foodborne Illnesses
The Office of Surveillance and Epidemiology (OSE) at the Kansas
Department of Health and Environment (KDHE) maintains the
surveillance system of notifiable diseases for the State of Kansas.
This passive surveillance system depends upon the timely and
accurate reporting of specific diseases by physicians, hospitals,
and laboratories in Kansas to the public health system as stated in
K.S.A. 65-118. Refer to Appendix B for a list of Reportable
Diseases in Kansas and a copy of the Kansas Notifiable Disease
Form. Foodborne illnesses are monitored through the statewide
surveillance system to assess disease impact, to detect trends, and
to guide interventions. OSE also collects and monitors reports of
outbreaks of gastrointestinal illness of unknown etiology.
Outbreaks of disease, regardless of the cause, or an unusual
occurrence of any disease, including those that appear to be
food-related or of public health concern, must be reported to KDHE
within four hours (K.A.R. 28-1-2). Epidemiology and Foodborne
Illnesses
Public health surveillance is the routine collection, analysis,
summarization, and dissemination of data for the purpose of
preventing and controlling the spread of disease.
An outbreak is an unexpected, unexplained increase of disease
occurring within a specific population at a given time and
place.
Epidemiology is defined as “the study of the distribution and
determinants of health-related states or events within a specific
population, and the application of this study to control health
problems.”
Last, JM ed. A Dictionary of Epidemiology, 3rd ed. New York:
Oxford U. Press, 1995:55.
Epidemiologists utilize the elements of surveillance, sound
science, and practical common sense to direct action for the
purpose of promoting and protecting the public’s health. Unlike
clinicians who care for the health of the individual,
epidemiologists focus on the health of the community. These
“disease detectives” collect data to answer the “who?”, “what?”,
”when?”, and “where?” of disease in the human population and
conduct analyses to answer the “why?” and “how?” to prevent future
disease. Infectious disease epidemiologists, in particular, study
the frequency and patterns of acute diseases, including foodborne
illnesses, to detect outbreaks and implement interventions to
prevent further illness.
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Laboratory Diagnosis of Foodborne Illnesses Most foodborne
infections are diagnosed through the identification of the pathogen
in stool collected from infected persons. Vomitus has also been
used to detect certain organisms and confirm the etiology. Blood
samples are recommended for the laboratory diagnosis of systemic
infections. Refer to Section 4 on Laboratory Analysis for more
detail about specimen collection, food sampling, and packing and
shipping of specimens for testing.
The following table provides a list of reportable diseases that
may be foodborne, their corresponding pathogen, recommended
specimens for laboratory diagnosis, and testing capabilities at the
Kansas Health and Environmental Laboratories (KHEL). Some diseases
require notification to KDHE within four hours, and some require
isolate submission to KHEL.
NOTIFIABLE FOODBORNE ILLNESSES AND CONDITIONS IN KANSAS
Disease or condition Pathogen Specimen DHEL Testing Bacterial
Anthrax (gastrointestinal)1 Bacillus anthracis Culture isolate By
request only Botulism (foodborne)1 Clostridium botulinum Blood,
stool Refer to CDC Brucellosis Brucella spp. Culture isolate By
request only Campylobacter infections Campylobacter spp. Stool
Routinely Cholera1 Vibrio cholerae Stool By request only
Escherichia coli O157:H7 (and other shiga-toxin producing E. coli,
also known as STEC)
Escherichia coli spp.2 Stool Routinely
Hemolytic Uremic Syndrome (HUS) Usually E. coli N/A N/A
Listeriosis Listeria monocytogenes Blood, spinal fluid By request
only Salmonellosis, including typhoid fever Salmonella spp.2 Stool
Routinely Shigellosis Shigella spp.2 Stool Routinely
Viral Hepatitis A3 Hepatitis A virus Blood By request only
Parasitic Amebiasis Entamoeba histolytica Stool Routinely
Cryptosporidiosis Cryptosporidium parvum Stool By request only
Cyclospora infection Cyclospora cayetanensis Stool By request only
Giardiasis Giardia lamblia Stool Routinely Trichinosis Trichinella
spiralis Blood Refer to CDC 1 Suspect or confirmed cases must be
reported to KDHE at (877) 472-7317 within four hours (K.A.R.
28-1-2) 2 Isolates must be sent to KHEL for further analysis
(K.A.R. 28-1-18) 3 Reporting suspect cases to KDHE at (877)
427-7317 is highly recommended NOTE: Outbreaks of disease,
regardless of the cause, must be reported to KDHE at (877) 472-7317
within four hours (K.A.R. 28-1-2).
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Pulsed-field Gel Electrophoresis (PFGE) A laboratory technique
frequently used to assist the surveillance and investigation of
foodborne illness and outbreaks is pulsed-field gel electrophoresis
(PFGE). This technique creates a unique “DNA fingerprint” or PFGE
pattern for disease-causing bacteria isolated from infected
persons. These patterns may be compared at the local, state, and
national levels to identify potential outbreaks and to focus the
epidemiologic investigation of outbreaks. During the PFGE process,
restriction enzymes are used to separate the bacterial DNA into
different sized fragments. Pulsing electric currents then move the
DNA fragments through a porous agarose gel. Smaller fragments move
quickly through the gel while larger fragments move more slowly.
The different fragments form a unique “DNA fingerprint” or band
pattern for each bacterial isolate. These PFGE patterns may be
analyzed to determine if the patterns are similar or
indistinguishable and may provide additional information during
investigations. Human isolates with indistinguishable PFGE patterns
warrant further investigation to identify any potential
epidemiological links among the infected individuals. PFGE may also
be conducted using bacterial isolates from food, and the patterns
may be compared with those of the human isolates. The following
image is an example of the “DNA fingerprint” of seven Salmonella
isolates. The vertical lanes with a numeric label represent the
PFGE pattern of a single isolate. The lanes labeled with a “C” are
the control lanes. Isolates #4 and #7 appear to have PFGE patterns
that are indistinguishable. Follow-up should be conducted with the
individuals from whom these bacterial isolates originated to
determine if the individuals have any potential epidemiological
links.
C 1 2 3 C 4 5 6 7 C
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Food Handlers, Foodborne Illnesses, and Public Health Food
handlers are persons who directly handle or prepare food. They may
work as paid employees or volunteers, serving food in a variety of
settings: food establishments, health care facilities, day cares
and schools, community functions, etc. Therefore, food handlers
have an important responsibility to follow safe food preparation
and handling practices to prevent illness. Though food handlers are
not at higher risk for developing a foodborne illness compared to
other persons, food handlers are at higher public health risk for
spreading pathogens. Infected food handlers, in particular,
represent an extremely high risk for the transmission of pathogens
to others through food when bare hand contact with ready-to-eat
foods and poor hand washing are present. The following tables are
lists compiled by the Centers for Disease Control and Prevention
(CDC) of (1) the pathogens often transmitted by infected food
handlers and (2) the pathogens occasionally transmitted by infected
food handlers1. Also included are the KDHE reporting requirements
for the corresponding disease.
Pathogens Often Transmitted by Food Contaminated By Infected
Food Handlers
Pathogen Notifiable Disease in KS Norovirus No Hepatitis A virus
Yes Salmonella Typhi Yes Shigella spp. Yes Staphylococcus aureus No
Streptococcus pyogenes No Submission of isolate to KHEL is required
per K.A.R. 28-1-18.
Outbreaks of disease, regardless of the cause, must be reported
to KDHE at (877) 427-7317 within four hours (K.A.R. 28-1-2).
1 Centers for Disease Control and Prevention. “Diseases
Transmitted Through the Food Supply”. Federal Register: November 6,
2003 (Volume 68, Number 215)
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Pathogens Occasionally Transmitted by Food Contamination by
Infected Food Handlers
Pathogen Notifiable Disease in KS Campylobacter jejuni Yes
Cryptosporidium parvum Yes Entamoeba histolytica Yes
Enterohemorhagic Escherichia coli Yes Enterotoxigenic Escherichia
coli Yes Giardia lamblia Yes Non-typhoidal Salmonella Yes Taenia
solium No Vibrio cholerae 01 Yes Yersinia enterocolitica No
Submission of isolate to KHEL is required per K.A.R. 28-1-18.
Because of the potential for food handlers to transmit pathogens
through the food they serve, restriction and exclusion requirements
have been established for infected food handlers in Kansas.
Employees who are excluded cannot work in any capacity in the food
establishment until written medical documentation is provided,
stating that the person is free of the infectious agent of concern.
Employees who are restricted can continue to work in the food
establishment, but cannot work with exposed food, clean equipment
utensils and linens, or unwrap single-service and single-use
articles until restrictions have been removed. According to the
2005 Kansas Food Code, food handlers who are diagnosed with an
illness due to norovirus, Salmonella Typhi, Shigella spp.,
Enterohemorrhagic or Shiga toxin producing E. coli, or hepatitis A
virus should be excluded from working in a food establishment. Food
handlers suffering from diarrhea, fever, vomiting, jaundice, or
sore throat with fever or have a positive stool result for
Salmonella Typhi or Escherichia coli O157:H7 should be restricted
from food handling, but can serve in another capacity within a food
establishment. More information about exclusion and restriction
requirements for certain health conditions is available in Appendix
D.
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Section 2
FOODBORNE DISEASE OUTBREAKS
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FUNDAMENTAL CONCEPTS OF FOODBORNE DISEASE OUTBREAKS Defining a
Foodborne Disease Outbreak In Kansas, a foodborne disease outbreak
is defined in the following ways:
1. Two or more individuals (from different households) who
experience a similar illness after eating a common food1 or food
from a common place. Household members generally share many meals
together and experience close personal contact with one another.
Therefore, similar illness among members of a single household is
not considered to be an outbreak.
2. An unexplained, unexpected increase of a similar illness, and
food is a likely source.
Further investigation to identify the source of infection should
be done. For example, an increased number of Campylobacter jejuni
identified at the state laboratory may suggest that a foodborne
disease outbreak has occurred.
Contact KDHE at (877) 427-7317 if an outbreak has occurred or if
assistance is needed in determining if an outbreak has
occurred.
NOTE: Positive laboratory identification of the disease-causing
organism is not necessary to determine that a foodborne disease
outbreak has occurred nor is this identification needed to begin an
investigation. Many foodborne disease outbreaks have been
recognized and investigated even in the absence of any laboratory
testing, positive laboratory results, or a definitive diagnosis.
Nonetheless, laboratory testing of clinical specimens and food
samples to confirm the pathogen of a foodborne disease outbreak
should always be a priority. Refer to Section 4 for more
information about laboratory testing. Identifying Foodborne Disease
Outbreaks Foodborne disease outbreaks may be identified from the
following:
• Foodborne illness complaints from private citizens • Medical
evaluations of ill individuals from healthcare professionals at
hospitals, clinics,
or physician offices • Routine surveillance and case
investigation of reportable diarrheal illnesses by
epidemiologists and public health nurses at state and local
health departments • Routine laboratory testing and techniques,
including PFGE, conducted by microbiologists • Information received
through the media and public information officers • Reports from
state and federal food safety regulators and environmental health
specialists
1 Food may also include ice, milk, juices, and other liquids
that are consumed.
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Reasons for Investigating Foodborne Disease Outbreaks Once a
foodborne disease outbreak has been identified, an outbreak
investigation should be implemented for the following reasons:
• To identify the cause, the risk factor(s), or source of
infection • To implement interventions or corrective actions to
prevent others from becoming ill • To fulfill statutory obligations
and respond to public and political concern • To evaluate existing
recommendations or strategies for preventing similar outbreaks • To
learn more about the public health implications of foodborne
pathogens
Three Components of a Foodborne Disease Outbreak Investigation
Foodborne disease outbreak investigations are conducted to
determine what factors are associated with illness and what
measures can be done to prevent further illness. This is achieved
through (1) an epidemiologic investigation, (2) laboratory
analysis, and (3) an environmental assessment. A thorough outbreak
investigation cannot be conducted without these three components,
which are often performed simultaneously. See Sections 3, 4, and 5
for more detail about the three components.
Roles and Responsibilities in a Foodborne Disease Outbreak
Investigation Successful foodborne disease outbreak investigations
depend upon the coordination and collaboration of key personnel. In
most outbreak investigations, the core investigative team is
comprised of the local health department infection control nurse,
the food inspector, a medical investigator, an epidemiologist, and
a microbiologist. Depending on the scope and size of an outbreak,
the investigative team may include more or fewer investigators, and
the different roles and responsibilities may overlap. Nonetheless,
the outbreak investigators should work together to ensure that all
necessary tasks are completed.
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Local Health Department (LHD) Infection Control Nurse • Oversee
all infectious conditions and outbreaks within the county • Conduct
initial investigation of potential outbreaks • Administer
interviews with persons associated with outbreaks • Distribute
stool kits and collect clinical specimens to obtain a diagnosis •
Submit clinical specimens and food samples collected for laboratory
testing • Maintain correspondence and collaborate with local
healthcare professionals • Implement control and prevention
measures as needed to stop the spread of infection • Provide
educational information about infectious conditions and control and
prevention
measures • Coordinate with food inspector, medical investigator,
and epidemiologist • Coordinate with local law enforcement at
earliest suspicion of intentional contamination
Food Inspector or Environmental Health Specialist
• Conduct inspection of food establishments • Identify and
address food safety issues that may have contributed to the
outbreak • Interview managers and food handlers about any illness
experienced and their specific
job duties • Collect food and environmental samples, if feasible
• Obtain menu of food items served • Enforce state restriction and
exclusion regulations related to food handlers • Perform Hazard
Analysis and Critical Control Points (HACCP) investigation, if
needed • Coordinate with LHD infection control nurse and medical
investigator or epidemiologist
Medical Investigator or Regional Coordinator
• Serve as a liaison between the LHD and KDHE • Assist LHD
infection control nurse with disease surveillance and investigation
• Provide technical guidance and overall support to an outbreak
investigation • Facilitate communication between LHDs during
inter-county outbreak investigations • Coordinate with LHD
infection control nurse, epidemiologist, and food inspector
Epidemiologist
• Assist in determining if an outbreak has occurred and if an
investigation is needed • Serve as lead investigator or primary
coordinator in an outbreak investigation • Facilitate and guide the
steps in an outbreak investigation • Provide technical,
statistical, and overall support to an outbreak investigation •
Coordinate with LHD infection control nurse, medical investigator,
food inspector, and
microbiologist • Maintain communication channels between
programs, agencies, counties, and states, as
needed • Oversee multi-county or multistate outbreaks •
Coordinate with CPHP at the earliest suspicion of an intentional
contamination
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Microbiologist • Test clinical specimens or food samples to
verify or confirm the diagnosis of the outbreak • Conduct further
subtyping or laboratory analysis, if appropriate • Coordinate with
reference laboratories at other state or federal laboratories •
Coordinate with LHD infection control nurse, medical investigator,
or epidemiologist • Maintain chain of custody for outbreaks of
suspected intentional contamination
Other important roles that may or may not be needed for a
particular investigation include the following: Physician /
Healthcare Provider
• Report notifiable diseases, including outbreaks, to local or
state health department • Provide clinical information and
diagnosis for patients when available • Assist in the collection of
clinical specimens for laboratory testing
Administrator (LHD)
• Fulfill the role of infection control nurse if needed • Assist
the LHD staff with outbreak investigations • May serve as the main
liaison with local physicians, the media, or KDHE • Enforce
statutes and regulations related to the health of residents,
investigation of causes
of disease, and prevention of spread of diseases within the
county Local Health Officer
• Serve as medical consult to county staff • Enforce statutes
and regulations related to the health of residents, investigation
of causes
of disease, sanitation inspections, and prevention of spread of
diseases within the county Public Information Officer
• Deliver clear, consistent messages related to diseases and
outbreaks • Respond to media requests related to diseases and
outbreaks • Provide educational information to the general
public
Federal Personnel1
• Provide guidance in national outbreaks or tracebacks • Assist
multistate outbreak investigations
1 Federal personnel that may be involved in a foodborne disease
outbreak investigation include the Centers for
Disease Control and Prevention, the U.S. Department of
Agriculture, the Food and Drug Administration, and the
Environmental Protection Agency.
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In the event of an intentional contamination of food, the
following personnel and agencies may also be called upon during an
outbreak investigation: Law Enforcement
• Coordinate with public health during initial threat assessment
and investigation • Contact and coordinate with Federal Bureau of
Investigation • Conduct criminal investigation • Ensure collection
of evidence in manner that is admissible in court
Emergency Management
• Coordinate efforts of all responding agencies • Provide
additional supplies, if needed
The Importance of Confidentiality Each of the key players in
outbreak investigations has the crucial responsibility of
maintaining confidentiality of the individuals involved in the
outbreak. Identifying information should never be released unless
absolutely necessary to properly conduct the outbreak investigation
and to protect the public’s health. Extreme consideration should be
taken to ensure that information is released only on a
“need-to-know” basis.
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30
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Section 3
THE EPIDEMIOLOGIC INVESTIGATION
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CONDUCTING AN EPIDEMIOLOGIC OUTBREAK INVESTIGATION The main
objectives of an epidemiologic outbreak investigation are (1) to
identify a problem, (2) to collect information related to the
problem, and (3) to develop conclusions and recommendations for
prevention and control. Illness and exposure histories are
collected, usually using questionnaires, and comparisons are made
between persons who became ill and those who did not. Conclusions
about the outbreak are then formulated from the epidemiologic data,
in conjunction with the results of the laboratory analysis and
environmental assessment. The following table lists the essential
steps of an epidemiologic outbreak investigation.
Steps of an Epidemiologic Outbreak Investigation 1. Determine
that an outbreak has occurred. 2. Contact and coordinate with key
personnel. 3. Obtain clinical specimens and food samples for
laboratory testing. 4. Implement control and prevention measures.
5. Define cases and conduct case finding. 6. Describe the outbreak
by time, place, and person. 7. Develop possible hypotheses. 8. Plan
and conduct an epidemiologic study to test hypotheses. 9. Analyze
the data collected and interpret results. 10. Report the findings
of the outbreak investigation.
The order presented in this manual reflects the logical process
of most outbreak investigations conducted in Kansas. However, each
outbreak is unique and the investigation should be conducted in a
way that ensures that all steps are completed. Several steps may be
and sometimes should be conducted simultaneously, emphasizing the
importance of a teamwork approach. For instance, control and
prevention measures should be implemented as soon as the source of
the foodborne outbreak is identified. Nonetheless, the first step
in any investigation should be determining if an outbreak has
occurred.
Good, self-study computer-based learning modules may be
downloaded from www2a.cdc.gov/epicasestudies/dwnload_case.htm.
33
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STEP 1. Determine that an outbreak has occurred. The most
important step in any outbreak investigation is to answer the
following question:
“Has an outbreak occurred?”
Most reports of foodborne illness are sporadic and are often not
associated with a recognized outbreak. The information collected
during the initial report may help determine if a foodborne illness
complaint is suggestive of an outbreak and whether or not an
outbreak investigation is necessary. This preliminary information
may also provide important clues about the cause and source of the
outbreak and will help guide the direction of the investigation.
Depending upon who receives the initial foodborne illness
complaint, a LHD nurse, food inspector, medical investigator, or
epidemiologist is an appropriate person to collect this initial
information. Detailed information that should be collected as soon
as possible includes, but is not limited to, the following:
• Information about the person reporting the potential outbreak
• Number of persons reporting illness • Date and time of illness
onset for each ill person • Specific symptoms experienced • Number
of doctor visits and hospitalizations • Number of stool samples
collected for testing
o Recommend testing if not yet done o Testing may still be
beneficial even if symptoms have ceased
• Specific diagnosis identified, if known • Total number of
persons exposed, both ill and not ill • Date and time food was
consumed • Location where food was prepared and eaten • Specific
food or drink consumed, including ice • Other commonalities,
including other shared meals or activities
o Earlier shared meals may be a source of infection • Additional
information, including specific activities and medications taken
before the
onset of illness o Other factors besides food may have
influenced illness
• List of contact information of all persons exposed The LHD
nurse or outbreak investigator may use the “Enteric Outbreak
Worksheet” and “List of Individuals Affected” Template in Appendix
B to capture much of this information. Food inspectors may use the
“Complaint Investigation Report” in Appendix D, which is provided
by the KDHE Bureau of Consumer Health. As mentioned in Section 2 ,
a foodborne disease outbreak is defined as two or more individuals
(from different households) who experience a similar illness after
eating a common food or different food from a common place. If only
one person reports illness or if only one household is affected,
then the report should be handled as a foodborne illness complaint.
If one or more
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similar reports of illness from different households are
received, then the definition of an outbreak has been met, and the
steps of an outbreak investigation should be conducted. In some
instances, the LHD nurse or outbreak investigator may detect a
foodborne outbreak through routine surveillance and observing an
unexplained, unexpected increase of a similar illness. This
situation suggests the need for further investigation to determine
the potential sources of infection. Completion of the “Enteric
Disease Supplemental Form” in Appendix B or the disease-specific
investigation form should be administered to collect pertinent
information. Medical investigators or epidemiologists at KDHE are
available at (877) 427-7317 to assist infection control nurses or
food inspectors with determining if an outbreak has occurred.
When verifying the existence of a foodborne outbreak, other
reasons for the increased illness should also be considered,
including changes in surveillance criteria, improved reporting, or
the introduction of new or revised laboratory detection
methods.
STEP 2. Contact and coordinate with key personnel. Once the
existence of an outbreak is verified, the next step is to answer
the following question:
“Who needs to know that an outbreak has occurred?” Because of
the nature of outbreak investigations, personnel who fulfill key
roles in an outbreak investigation should be notified as soon as
possible. A successful investigation requires a teamwork approach
and collaboration among, but not limited to, medical investigators,
epidemiologists, infection control nurses, food inspectors,
microbiologists, healthcare providers, regulators, and the media.
Occasionally, foodborne outbreaks may involve individuals in a day
care or an adult care setting, and personnel from these entities
should also be notified. Most communication will occur between the
LHD infection control nurse, the food inspector assigned to the
outbreak, the regional medical investigator and an epidemiologist.
Depending upon the county affected and the source of the food
(i.e., licensed food establishment, retail food establishment, or
food processing plant), food inspectors at contract counties or
state agency may need to be contacted. Medical investigators and
epidemiologists at KDHE are available at (877) 427-7317 to assist
with coordination and communication of key personnel, especially
between state and federal entities. The table on the following page
lists the agencies that may be involved in an outbreak
investigation. This list is by no means exhaustive. Communication
and collaboration with individuals within these agencies should be
established prior to an outbreak occurring.
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List of Agency Contacts
Agency Phone No. When to Contact Local Health Departments (LHDs)
Communicable Disease See directory For all outbreaks Environmental
Health See directory If food establishment‡ is involved
Administration See directory If needed
Kansas Department of Health and Environment (KDHE)
Epidemiologic Services (877) 427-7317 For all outbreaks Food
Safety and Consumer Protection (785) 296-5600 If a KDHE-regulated
establishment
is involved* Diagnostic Microbiology Laboratory (785) 296-1633
If specimens are submitted Child Care Licensing and Registration
(785) 296-1270 If day care is involved Public Information (785)
296-5795 If needed
Kansas Department on Aging (KDOA) Complaint Program (785)
296-1265 If nursing home, adult care, or
long-term care facility is involved Kansas Department of
Agriculture (KDA) Retail Food Inspection Program (785) 296-3511 If
KDA-regulated establishment is
involved** Laboratory Program (785) 862-0108 If needed Public
Information (785) 296-2653 If needed
Centers for Disease Control and Prevention (CDC) Outbreak
Response and Surveillance Team (404) 639-2198 If needed
Food and Drug Administration (FDA) Kansas City District Office
(913) 752-2100 If a traceback is involved
U.S. Department of Agriculture (USDA) Food Safety and Inspection
Service (FSIS) Office of Public Health Science
(402) 344-5162 If a traceback is involved
The Kansas Public Health Directory is found at
www.kdhe.state.ks.us/olrh/download/health_directory.pdf‡ See
Appendix A – Glossary of Terms for definitions. *The Food
Protection and Consumer Safety Program at KDHE regulates
stand-alone restaurants, school food
service operations, senior meal sites, and mobile food units.
**The Retail Food Inspection Program at KDA regulates grocery
stores, restaurants in grocery stores,
convenience stores, food wholesalers and warehouses, food
processers, and food manufacturers.
36
http://www.kdhe.state.ks.us/olrh/download/health_directory.pdf
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Once an outbreak has been identified, the other two components
of an investigation, Laboratory Analysis and Environmental
Assessment, should be initiated. Refer to Sections 4 and 5 for
information about these components.
STEP 3. Obtain clinical specimens and food samples for
laboratory testing. The question to be answered in Step 3 is the
following:
“What is the organism that has caused illness?” For most
foodborne disease outbreaks, stool samples are collected from
persons experiencing diarrhea to identify or confirm the pathogen.
Blood cultures or serology testing are recommended for systemic
infections, such as Listeria monocytogenes or hepatitis A virus.
However, serology is less useful for most other foodborne
illnesses. When collecting clinical specimens for testing, keep the
following in mind:
• Stool collection should be encouraged whenever a person is
experiencing or has recently experienced a diarrheal illness. If
possible, requests for stool samples should begin during the
initial foodborne illness report, and such requests may continue
throughout the outbreak investigation.
• Testing of all ill individuals is not useful nor is it a good
utilization of resources. Collection of five specimens is usually
sufficient to confirm the diagnosis.
• Laboratory testing may still be beneficial even after symptoms
have ceased. For many foodborne illnesses, an ill person may
continue to shed the pathogen in their stool even a few days after
symptoms have disappeared and stool appears normal.
• Laboratory testing of individuals who are not ill is not
routinely recommended, except when required to remove specific
exclusion or restriction guidelines.
• Even in the absence of any laboratory confirmation, positive
results, or definitive diagnosis, pathogens may still be implicated
and public health measures may be implemented solely based on
information collected during the outbreak investigation.
The pathogen, specifically bacteria or bacterial toxins, may
also be identified through food samples. Viral and parasitic
identification is extremely difficult. However, food samples will
generally not be tested until the investigation yields a specific
food or set of foods suspected and a specific pathogen identified
by clinical specimens. Refer to Section 4 for more information
about collecting clinical specimens and food samples.
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STEP 4. Implement control and prevention measures. Although the
source or the cause of the outbreak may remain unknown, the
following question should be addressed:
“What can be done now to stop the spread of infection?”
Investigators should respond and implement appropriate public
health action as soon as possible. Important control and prevention
measures related to foodborne disease outbreaks may include, but
should not be limited to, the following:
• Removal of contaminated food • Exclusion and restriction of
persons who are at high risk of spreading illness, including
food handlers, day care attendees and providers, and persons
involved with direct patient care
• Emphasizing good handwashing • Closing the food establishment,
if implicated and necessary
As more information becomes available, corresponding measures
should also be taken as needed:
• Hosting conference calls with key agencies and investigators
to discuss and coordinate the public health response
• Sending notices to healthcare professionals, schools,
daycares, or nursing homes and other entities about the public
health recommendation
• Developing a press release to educate the public about
protecting oneself from foodborne illness
STEP 5. Define cases and conduct case finding. Important
questions to ask at this stage in an outbreak investigation are the
following:
“What criteria should be used to determine if an ill person is
part of an outbreak?” “Who else is ill?”
Outbreaks and their corresponding investigations can quickly
become complex. As a result, it is important to establish a clear
understanding of the outbreak as early as possible. Organizing the
preliminary information will help in the development of a case
definition and may also provide clues about the pathogen and its
transmission. Line list A line list or line listing is a table or a
spreadsheet that summarizes information about persons who may be
associated with an outbreak. Each row or observation represents a
single individual, and each column represents a variable or a
specific characteristic about the person. Column
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information often includes identifying information, demographic
information, clinical information, and other epidemiologic
information, including risk factors possibly related to illness.
Preliminary information obtained during the early stages of an
outbreak investigation can be organized using a line list. As the
investigation progresses, the line list can be updated with any
additional information that is collected. Line List Example
ID Name Age Sex Ill OnsetD OnsetT D N V C Wed 1 G.H. 45 F Y July
1 1:00a Y Y Y N Y 2 C.T. 57 F Y June 30 11:00p Y Y N Y Y 3 T.M. 39
M Y June 30 11:45p Y N N Y Y 4 B.O. 32 M N N N N N Y 5 R.A. 27 M N
N N N N Y 6 D.S. 16 M Y June 30 6:00a N Y N Y Y
Key:
ID: Identification number Name: Age:
Person’s initials Age in years
D: Diarrhea (3 or more loose stools in a 24-hour period)
Sex: Female or Male N: Nausea Ill: Reported illness V: Vomiting
OnsetD: Date of illness onset C: Abdominal Cramping OnsetT:
Time of illness onset
Wed: Attended wedding reception on Saturday, June 29
This line list shows that four ill individuals experienced
similar symptoms around the same time period. In addition, they all
attended the same wedding. Based on this information, it is highly
likely that these individuals became ill after eating something
served at a wedding reception they attended two days earlier.
Line listings are working documents that are important for
organizing information during an outbreak investigation. They are
used to identify the criteria that may be included in a case
definition, to arrange detailed data about those affected, and to
provide a “bird’s-eye view” of the outbreak. Refer to Appendix B to
learn more about creating a line listing.
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Case definition A case definition is a set of criteria for
determining who should be classified as a “case”, or a person with
the particular item(s) of interest. The case definition in the
setting of an outbreak investigation usually includes four
criteria: clinical information and information related to time,
place, and person. A case definition should be developed for every
outbreak to ensure that ill persons are classified appropriately.
Good case definitions often include simple and objective clinical
criteria (e.g., diarrhea defined as three or more loose stools in a
24-hour period, vomiting, or nausea with a fever ≥ 101ºF).
Laboratory confirmation may also be a criterion for classifying an
ill person as a case. The criterion for time includes onset of
illness during a specific time period (e.g., onset of illness in
the past two weeks or onset of illness after June 15). For the
place criterion, the case definition may include the location of
exposure or the community the ill persons reside or work (e.g.,
Shawnee county or Curtis State Office Building). Regarding the
person criterion, the case definition may focus on individuals with
certain characteristics (e.g., persons who attended an event).
Early on in an investigation, it may be worthwhile to have a more
inclusive case definition or several case classifications (e.g.,
confirmed, probable, or suspect). Such flexibility allows the
investigator to better characterize the extent of the outbreak, to
identify more persons potentially affected, and to start
formulating hypotheses. For example, a case might be classified as
confirmed if laboratory confirmation of the disease is available
and if the time, place, and person criteria have been met. A case
that exhibits the typical clinical characteristics of the disease
and meets the time, place, and person criteria, but has no
laboratory confirmation, might be considered a probable case. A
case with some, but not all, of the criteria might be classified as
a suspect case. As more information becomes available, the case
definition can be refined to ensure that the definition is as
specific as needed and that as many of the “actual” cases are
captured. Unfortunately, no case definition is 100% accurate, and
persons with a mild infection may be missed.
Regardless of what criteria are used or the number of case
classifications developed, the case definition should be applied
consistently and without bias to all persons under investigation.
Also, the definition should not include any exposure or risk factor
that will later be evaluated or analyzed.
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Case Definition Example Component of definition Question asked
Factual item Clinical criteria What were the predominant symptoms?
Acute onset of gastroenteritis Time When did infection occur?
Saturday evening Place Where did infection occur? Wedding reception
Person Who may have been affected? Wedding attendee
Using the information from the line list presented earlier, a
case may be defined as “an illness in any person who experienced an
acute onset of gastroenteritis after attending the wedding
reception on Saturday, June 29”. Persons with ID numbers 1, 2, 3,
and 6 may be considered cases based on this proposed definition. If
the definition is later refined to state that a case is “an illness
in any person who experienced diarrhea or vomiting after attending
the wedding reception on Saturday, June 29”, then only persons with
ID numbers 1, 2, and 3 will be classified as a case for this
outbreak. Person with ID number 6 did not report diarrhea or
vomiting, therefore does not meet the refined definition of a case.
The line list has been updated to include a variable labeled
“Case”. Each person has been assigned a “Y” or an “N”, depending on
if the person met the refined case definition or not.
ID Name Age Sex Ill OnsetD OnsetT D N V C Wed Case 1 G.H. 45 F Y
July 1 1:00a Y Y Y N Y Y 2 C.T. 57 F Y June 30 11:00p Y Y N Y Y Y 3
T.M. 39 M Y June 30 11:45p Y N N Y Y Y 4 B.O. 32 M N N N N N Y N 5
R.A. 27 M N N N N N Y N 6 D.S. 16 M Y June 30 6:00a N Y N Y Y N
Case finding When an outbreak is first recognized, investigators
should attempt to “cast the net wide” to determine the extent of
the outbreak and identify additional cases. Case finding methods
might include the following:
• Asking affected persons to provide the names and contact
information of other ill persons • Directly contacting physicians’
clinics, hospitals, laboratories, schools, or nursing homes,
as appropriate • Alerting the public directly if needed to
protect the public’s health
The data obtained during case finding can provide clues about
the outbreak and potential risk factors associated with illness.
The “Enteric Disease Supplemental Form” in Appendix B may be used
to systematically gather information from the ill persons,
including identifying information, demographic information,
clinical information, and risk factor information.
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STEPS 6 – 10 describe steps that LHDs in Kansas may rely on KDHE
medical investigators and epidemiologists for assistance, if
needed. LHDs may elect to perform these steps themselves if
resources permit.
STEP 6. Describe the outbreak by time, place, and person.
“What information about the outbreak is available thus far?”
Descriptive epidemiology should be performed to describe the
information about the outbreak. As new and updated information
becomes available during the course of an investigation, this
process may need to be repeated. Tools that are used to organize
and depict the outbreak by time, place, and person include epidemic
curves, maps, and frequency tables. Epidemic Curves An epidemic
curve (epi curve, for short) is a special type of histogram that
provides a visual depiction of the outbreak and offers information
related to time. An epi curve provides information about the extent
of the outbreak, the potential period of exposure, and the possible
mode of transmission. Investigators use an epi curve to determine
where they are in the course of an outbreak – is the outbreak on an
upswing, on the down slope, or has the outbreak ended? An epi curve
also helps filter out “background noise” or outliers that may be
“red herrings” and are not associated with the outbreak. Most
often, an epi curve plots the incubation period or date of onset of
illness on the x-axis and the number of ill persons or cases on the
y-axis. (NOTE: The maximum time period on the x-axis should not
exceed ¼ to ⅓ of the incubation period, if the incubation period is
known.) If the number of cases increases, then new cases are likely
to appear in the future and the outbreak is continuing. On the
other hand, if the number of cases begins to dwindle, then the
outbreak has peaked and is coming to an end. Such information can
aid investigators in determining what measures should be taken.
Refer to Appendix B for more information about how to create an
epidemic curve. The following page describes the three main types
of outbreaks which may be visually displayed through epi curves:
common-source or point-source outbreaks, propagated-source or
person-to-person outbreaks, and continual-source outbreaks.
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Common-source or point-source outbreaks occur when individuals
are exposed to some source of infection at the same time. An
example of a point-source foodborne disease outbreak is illness
experienced by guests who attended and ate food served at the same
wedding reception. Foodborne disease outbreaks are most often
point-source outbreaks.
01
2
34
56
7
89
10
10/1 10/2 10/3 10/4 10/5 10/6 10/7
Date of Onset
Num
ber o
f Cas
es
Propagated-source or person-to-person outbreaks person to
another via the fecal-oral route. An enoroviral infections within a
nursing home. Infecbecause of poor handwashing and inadequate
disinfec
0123456789
10
10/1 10/2 10/3 10/4 10/5 10/6 10/7
Date of Onset
Num
ber
of C
ases
Continual-source outbreaks occur when a source rembe exposed to
this source. An example of a conticontinues to use water obtained
from a contaminated
0
1
2
3
4
5
6
7
8
9
10
10/1 10/2 10/3 10/4 10/5 10/6 10/7
Date of Onset
Num
ber o
f Cas
es
Epidemic curves of common-source outbreaks are characterized by
a sharp rise in the number of cases that slowly tapers off. Most
illness appears within one incubation period.
occur when infection is spread from one xample of a
person-to-person outbreak is tion spreads from one resident to
another tion.
Epidemic curves of propagated outbreaks are characterized by
progressive peaks, approximately one incubation period apart.
ains contaminated and persons continue to nual-source outbreak
is a community that well.
Epidemic curves of continual-source outbreaks are characterized
by a gradual rise in cases that often plateaus.
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Maps and pictures Maps and pictures are helpful in showing the
geographical location or layout of the place in which an outbreak
has occurred. This spatial information may be crucial to the
outbreak investigation and may provide clues about the source of
the outbreak. The “spot map” is a well-used pictorial of the
spatial distribution of illness within a specific setting or area.
In the following example of a spot map, ill individuals are plotted
onto a map, with each point representing the residence of an
individual. The cluster of cases may indicate a local exposure in
the community. Other spot maps, such as place of employment or
school attended, may be useful in some situations.
Frequency Tables Frequency tables may be used to summarize the
different attributes of the cases and may provide information
related to person. A special characteristic identified among a
majority of the cases may assist the investigators with potential
exposures. Frequency Table Example
Characteristic No. of Cases (%) Age, < 1 yr 15 (30) Age, 1 to
4 yrs 25 (50) Age, 5 to 19 yrs 5 (10) Age, 20 to 49 yrs 5 (10) Age,
50+ yrs 0 (0) Sex, Male 28 (56)
This table shows that of the 50 cases identified, 80% are under
the age of five years. Investigators should consider exposures that
affect mainly persons of this age group, such as foods or drinks
most often eaten by children.
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STEP 7. Develop possible hypotheses After the preliminary
information has been organized, the next question to answer is the
following:
“What educated guesses can be made?” A hypothesis is an educated
guess about the cause of the outbreak and the factors that may have
contributed to illness. Investigators develop possible hypotheses
to guide the direction of the investigation and to initiate
appropriate control measures. In most instances, investigators
begin to formulate hypotheses during the initial phone call and
continue to refine these hypotheses as more information becomes
available. The symptoms experienced, the incubation period, the
recovery period, the food items served, the biological plausibility
of pathogens, and the tools used to organize the outbreak
information provide invaluable clues about the source and cause of
illness. The sooner those hypotheses are developed, the sooner that
public health interventions may be implemented. Hypotheses may need
to be revised during the outbreak investigation, as new information
becomes available.
Appendix E provides a table that lists foodborne illnesses and
their corresponding incubation periods, signs and symptoms,
recovery periods, and foods typically associated with illness. This
table may be useful in developing hypotheses related to foodborne
disease outbreaks.
STEP 8. Plan and conduct the epidemiologic study to test
hypotheses. STEP 8 is the focal point of any epidemiologic outbreak
investigation. It involves a systematic way of evaluating the
hypotheses already developed, of collecting more information about
the illness and outbreak, and of answering the following
questions:
“Why and how did illness occur?” “What external factors or
exposures were associated with illness?”
The STEPS conducted thus far have focused on the ill persons.
However, a thorough outbreak investigation depends upon comparing
exposures or risk factors among those who are ill and those who are
not ill. These comparisons help to determine what happened, to
identify what may have caused disease, and to recommend what can be
done to prevent illness in the future. The questionnaire and the
study design are important tools used to further analyze an
outbreak and make comparisons. Careful planning should be taken
when designing the questionnaire, determining the appropriate study
design, and organizing the logistics of carrying out the outbreak
investigation.
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Questionnaire The questionnaire is a set of questions that
captures detailed information from both ill and not-ill persons
associated with a foodborne disease outbreak. A questionnaire can
revolve around a specific event, a specific menu, or be generalized
for foods commonly eaten and establishments frequented. In many
instances, the questionnaire may serve as a means of finding more
cases and for developing hypotheses. In general, an epidemiologist
will be involved in producing an appropriate questionnaire. The
following are the main components of a questionnaire:
• Identifying information
o Name o Address o City, County, State, Zip code o Phone number
(day, evening, and cell)
• Demographic information o Age o Sex o Race o Occupation
• Clinical information o Specific symptoms experienced, if any o
Date and time of illness onset o Date and time of recovery or
duration of illness o Medical visits / hospitalizations o Specific
diagnoses
• Exposure or risk factor information o Information related to
specific food items consumed o Other potential exposures, including
specific activities
• Knowledge of illness in others
When possible, a menu should be obtained, and specific food
items, including ice, should be listed in the exposure or risk
factor section. This will help the respondent remember the food
items eaten.
Study Design Two types of studies that are often used in
foodborne disease outbreak investigations are retrospective cohort
studies and case-control studies. Retrospective Cohort Studies A
retrospective cohort study is often conducted for outbreaks
involving a well-defined group of individuals. The investigator
develops a questionnaire and retrospectively collects exposure and
illness information from all persons in the group. Each person
reports what exposures he or she had and whether or not he or she
became ill following the exposures. The investigator then
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analyzes the data collected to assess which exposure(s) are
associated with the highest risk of illness. For example, 150
individuals attended a wedding reception, and many of the attendees
consumed the food items served at this reception. A few days later
several attendees reported symptoms of diarrhea, vomiting, and
abdominal cramping. In this scenario, a well-defined group of
individuals attended and ate food at a wedding reception. Some of
the attendees subsequently reported illness following the shared
experience. Based on this information, the investigator may conduct
a retrospective cohort study to determine how many of the 150
persons experienced illness after the reception and to identify the
specific food item(s) associated with illness. Case-control Studies
A case-control study is appropriate for outbreaks in which
individuals are not part of a well-defined group of individuals.
During a case-control study, the investigator develops a
questionnaire that is to be administered to persons with disease
(“cases”) as well as persons without disease (“controls”). Both
groups of individuals are then asked to answer questions about
specific exposures they may have had. The investigator analyzes the
data and compares the odds of having an exposure among the cases
versus the odds of having an exposure among the controls. For
example, eight cases of Salmonella typhimurium were reported during
the same week in County X. Because County X normally observes one
salmonellosis case within a one-month period, the investigator
suspected that an outbreak had occurred. Case investigations were
conducted, and the preliminary information revealed that five of
the eight cases reported eating at Restaurant X before becoming
ill. In this scenario, the total number of persons at risk is
unknown and not well-defined. The investigator has no means of
knowing how many persons in the community may have eaten at
Restaurant X during a certain time period. Moreover, even though
five of the eight cases mentioned eating at this restaurant, the
association between illness and eating at Restaurant X has not yet
been well established. Based on this information, the investigator
may conduct a case-control study to determine if there is an
association between illness and eating at Restaurant X or if
another exposure may be linked with illness. Selecting controls in
a case-control study An essential component of the case-control
study is selecting controls with whom the cases may be compared.
Ideally, controls should be similar to cases except they do not
have the disease. Controls should also represent the same
population as the cases. If a certain exposure is reported more
often by cases than controls, then this exposure is considered to
be associated with illness.
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Controls may be found in the following ways: Credit card slips
from the food establishment, if one is implicated Neighbors or
individuals from the same community as cases Patients from the same
physician practice or hospital with a different disease diagnosis
Friends of cases Persons in the phone book who share the same phone
prefix
In the above case-control scenario, controls may be found in the
community where Restaurant X is located.
The following table highlights the key similarities and
differences between a cohort study and a case-control study used
during an outbreak investigation.
RETROSPECTIVE COHORT STUDY vs. CASE-CONTROL STUDY in OUTBREAK
INVESTIGATIONS
Retrospective Cohort Study Case-Control Study Similarities
Uses questionnaire to gather data Yes Yes Makes comparisons
between ill and not-ill persons
Yes Yes
Evaluates associations between risk factors and illness
Yes Yes
Differences
Population affected Well-defined Poorly defined or unknown Basis
for inclusion into study Common exposure Presence or absence of
illness
Question to be asked “Did you become ill?” “Were you
exposed?”
Statistical analysis Attack rates Food-specific attack rates
Relative Risk ratios Odds ratios, but less frequently
Odds Ratio
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Logistics When the questionnaire has been developed and the
study design has been selected, the logistics of carrying out the
investigation should be considered, including the following:
For a cohort study, a complete list of the group of individuals
and their contact information is needed
For a case-control study, the method for selecting controls
needs to be decided If possible, the questionnaire should be tested
for clarity prior to administration The personnel assigned to the
study should become familiar with the questionnaire and
any potential questions that may arise ― LHD nurses and local or
KDHE epidemiologists and medical investigators often share the task
of conducting interviews
A feasible method for administering and distributing the
questionnaire should be discussed ― self-administered or personal
interview? In person, by phone, by mail, by electronic mail, or via
the Internet?
The data entry program or spreadsheet and method of entering
data into the program should be considered
Once a plan of action has been developed, the outbreak study
should be initiated as soon as possible. It may occasionally be
necessary for phone calls to be made after hours or on the
weekends. The longer the time lapse between exposure and the
request for information, the poorer the quality of data that might
be collected. STEP 9. Analyze the data collected and interpret
results. After the data are collected, analysis and interpretation
of the data should be conducted to answer these questions:
“What do the data reveal?” “What can be concluded from all the
information collected?”
Important tasks that should be performed to finalize the data
include the following:
• Re-evaluate the case definition and ensure that persons
classified as cases meet the case definition
• Update any epidemic curves previously plotted • Calculate
frequencies and percentages • Compute the median and ranges for the
incubation period and recovery period • If the study design was a
retrospective cohort study, calculate the attack rate, food-
specific attack rates, and relative risk ratios • If the study
design was a case-control study, calculate the odds ratios •
Determine if results obtained are statistical significant (e.g.,
95% confidence
intervals)
More information about analyzing data obtained through a
retrospective cohort study or a case-control study may be found in
Appendix B.
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Following analysis of the data, the results should be
interpreted. Information gathered from the epidemiologic
investigation should be compared with the findings obtained during
the environmental assessment and the laboratory analysis. General
knowledge about foodborne illnesses should be collectively used to
help explain what happened, what measures should be taken
immediately, and what steps should be taken to prevent similar
situations from occurring in the future. STEP 10. Report the
findings of the outbreak investigation. Although the outbreak has
been contained, documentation is extremely important as a written
record of the public health rationale for the activities as well as
the findings of the investigation. Written reports answer the
following questions:
“What public health lessons can be learned from this outbreak?”
In addition to documentation of activities and findings, a written
report provides a record of performance, provides an account of the
outbreak for potential medical and legal issues, and can improve
the quality of future investigations. Proper reporting of the
investigation includes the following:
Completion of the CDC eFORS form in Appendix B and submission to
the Foodborne Disease Surveillance Coordinator at KDHE [Fax: (877)
427-7318]. This form is used to report foodborne outbreaks in
Kansas to the CDC for national surveillance purposes.
Preparing and writing a report that follows a scientific format
of introduction, background, methods, results, discussion,
recommendations, and supporting documents. Appendix B provides more
information about the final report. Because final reports can be
lengthy, a one-page preliminary or summary report should be
prepared and disseminated until the final report is completed.
Dissemination of the preliminary, summary, and final reports as
widely as needed. At a minimum, the submitter should retain a copy,
and additional copies should be provided to the outbreak
investigators (local and at KDHE) and any facility involved in the
outbreak. Synopses may also be used for press releases and postings
on websites. Publications in local, regional or statewide documents
offer wider review, allowing many others to learn from the
experience.
For outbreaks of intentional contamination, the dissemination of
information in the form of reports and press releases should be
coordinated with law enforcement officials.
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INTENTIONAL CONTAMINATION OF FOOD In an era of preparedness and
a heightened threat of terrorism, investigators must consider
intentional contamination of food when unintentional causes do not
seem plausible. From the epidemiologic perspective, the steps
required to detect, diagnose, and reduce foodborne illness and
outbreaks are the same ones required to prevent, identify, and
respond to a terrorist attack on food. Epidemiologists depend upon
science-based approaches to identify the cause, risk factor(s), or
source of infection and to implement interventions to prevent
others from becoming ill. Unfortunately, foodborne disease
outbreaks are common occurrences and attributing the cause of
illness to an intentional contamination event can be difficult.
Moreover, intentional events may involve diseases or
characteristics of diseases that are often investigated. A number
of clues may alert outbreak investigators to consider that a
foodborne disease outbreak might be intentional.
Epidemiologic Clues • Unusual agent or vehicle • Multiple
unusual or unexplained diseases in a single person • High attack
rate or severe outcomes or deaths • Failure of patients to respond
to conventional treatments • Multiple exposure sites or vehicles
with no apparent link • Many ill persons presenting near the same
time • Deaths or illness among animals that may be unexplained
and occur before illness in the human population
Law Enforcement Clues • Intelligence or threat information •
Unlawful possession of pathogens by an individual or
group • Evidence of a credible threat in a specific area •
Identification of literature pretaining to the development or
dissemination of particular agent
Source: International Association for Food Protection.
Procedures to Investigate Foodborne Illness. 5th ed. 1999.
Reprinted 2007.
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Investigators in both law enforcement and environment will also
have to work together to find the answers to the following
questions:
• How would perpetrators gain access to food? • How could a
pathogen be introduced? • How was the agent mixed or distributed? •
How might the pathogen spread in the environment?
Although the epidemiologic approach remains the same regardless
if the event is deliberate, these additional steps will need to be
performed during the investigation of an intentional foodborne
disease outbreak.
• Public health officials should work closely with law
enforcement and emergency management agencies at all levels if an
intentional event is suspected or identified.
• Local, state, and federal law enforcement agencies should be
notified and will be the lead agencies in investigating the
criminal activity.
• The KDHE Center for Public Health Preparedness (CPHP) should
be notified in addition to other state and local emergency
management agencies.
• Depending on the food vehicle and nature of the threat, other
federal agencies that should be notified include the Food and Drug
Administration, the U.S. Department of Agriculture, and the U.S.
Department of Homeland Security.
A strong and flexible public health infrastructure is the best
defense against any disease outbreak – naturally or intentionally
caused. As with all public health events, coordination and
cooperation among all agencies are critical to the success of any
response.
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Section 4
THE LABORATORY ANALYSIS
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LABORATORY ANALYSIS DURING OUTBREAK INVESTIGATIONS The main
objectives of laboratory analysis during outbreak investigations
are (1) to confirm the clinical diagnosis through identification of
the causative agent from human specimens, (2) to ensure proper
identification of the disease, and (3) to determine if the
causative agent is present in the implicated environmental source,
such as food. General Guidelines for Clinical Specimen
Collection
One of the most important factors in the identification of
etiologic agents responsible for foodborne disease outbreaks is the
collection of clinical specimens as early in the course of the
investigation as possible. Most foodborne infections are diagnosed
through the identification of the pathogen in stool collected from
infected persons. Vomitus has also been used to detect certain
organisms and confirm the etiology. Serology and blood cultures are
recommended for the laboratory diagnosis of systemic
infections.
Stool Specimens Proper collection of stool specimens requires
having stool kits readily available, using the appropriate kit for
the suspected disease, and encouraging ill persons to submit a
stool specimen. Types of Stool Kits The Kansas Health and
Environmental Laboratories (KHEL) provide (1) an enteric stool kit
and (2) an ova and parasite (O&P) kit.
Enteric stool kits contain a vial of modified Cary-Blair medium
(0.16% agar concentration). These kits are used to test for
Campylobacter spp., Salmonella spp., Shigella spp., Staphylococcus
aureus, Bacillus cereus, Clostridium perfengens, and Shiga toxin
producing E. coli for culture and identification. These kits may
also be used to test for norovirus and bacterial toxins. Testing
for norovirus at KHEL is conducted only in outbreak situations and
must be cleared by KDHE Epidemiologic Services at (877)
427-7317.
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O&P stool kits contain a vial of formalin and a vial of
polyvinyl-alcohol (PVA). These kits are used to identify intestinal
parasites, including Cryptosporidium parvum, Cyclospora
cayetanensis, Entamoeba histolytica, and Giardia lamblia. Testing
for Cryptosporidium parvum and Cyclospora cayetanensis at KHEL is
available, but must be requested.
Five sets of each kit (enteric and O&P) are recommended to
be kept on hand at each local health department. The kits have
expiration dates, so rotation or replacement is essential. A
“Universal Laboratory Specimen Submission Form” must also accompany
each kit. Distributing Stool Kits and Obtaining Stool Specimens The
following list describes the steps that a local investigator should
take to obtain stool specimens from ill persons.
1. Provide one stool kit to persons experiencing diarrhea,
defined as three or more loose stools within a 24-hour period. In
outbreak situations, stool specimens from five to eight ill
individuals are ideal.
2. Instruct the ill person to use newspaper, a bedpan, plastic
wrap, or aluminum foil to collect the stool specimen. The lining
should be placed under the toilet seat and pushed slightly down in
the center, but not touching the water, creating a “bowl” in which
the specimen may be collected. The person should pass feces
directly onto this lining. Prior to passing feces, the person
should try to urinate so as not to mix the fecal specimen with
urine.
3. If a bacteria, bacterial toxin, or norovirus is suspected,
provide one enteric kit. a. Collect a marble-sized mass of feces
and place into the specimen bottle containing
the Cary-Blair medium (media should be pink to red in color, if
not do not use). A plastic spoon or tongue depressor may be used to
collect the specimen.
b. Mix thoroughly by shaking the bottle vigorously after the
bottle cap has been tightened securely and keep refrigerated until
shipped.
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4. If a parasite is suspected, provide one O & P kit. a.
Collect two marble-sized specimens and place into each vial
(formalin and PVA).
The fecal material should be put in the preservative as soon as
it is passed. b. Mix both vials thoroughly and keep at room
temperature (do not refrigerate).
5. After the specimen has been collected, the person should
dispose of the excess material into the toilet and discard the
soiled lining.
6. Ask person(s) to return stool specimens to the health
department by mail or in person. 7. Contact KDHE Epidemiologic
Services at (877) 427-7317 and provide the
epidemiologist with the names of the persons for whom specimens
will be submitted for testing at KHEL.
8. Fill out the “Universal Laboratory Specimen Submission Form”
for each specimen obtained. Under the subheading “Submitter
Comments”, indicate that the specimen is associated with an
outbreak and that KDHE Epidemiologic Services has been notified.
Refer to Appendix C for complete instructions on filling out this
form and for associating the form with each specimen.
9. Refer to Appendix C for specific instructions on packing and
shipping enteric kits to KHEL.